U.S. patent application number 10/295983 was filed with the patent office on 2004-05-20 for dispersion, coating composition, and recording medium containing silica mixture.
This patent application is currently assigned to Cabot Corporation. Invention is credited to Brown, Steven E., Liu, Joanne, Morris, Michael D..
Application Number | 20040097631 10/295983 |
Document ID | / |
Family ID | 32297328 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040097631 |
Kind Code |
A1 |
Morris, Michael D. ; et
al. |
May 20, 2004 |
Dispersion, coating composition, and recording medium containing
silica mixture
Abstract
The invention provides an aqueous dispersion comprising fumed
silica particles, colloidal silica particles, and water. The fumed
silica particles have a BET surface area of about 70 to about 140
m.sup.2/g, and the colloidal silica particles have a BET surface
area of about 110 to about 150 m.sup.2/g. Also, the total amount of
silica in the dispersion is about 35% to about 60% by weight, and
the fumed silica particles comprise about 25% to about 80% by
weight of the total amount of silica in the dispersion. The
invention also provides a coating composition and a recording
medium incorporating the inventive dispersion.
Inventors: |
Morris, Michael D.; (Nashua,
NH) ; Liu, Joanne; (Lowell, MA) ; Brown,
Steven E.; (Tyngsboro, MA) |
Correspondence
Address: |
Michelle B. Lando
157 Concord Road
Billerica
MA
01821-7001
US
|
Assignee: |
Cabot Corporation
Billerica
MA
|
Family ID: |
32297328 |
Appl. No.: |
10/295983 |
Filed: |
November 15, 2002 |
Current U.S.
Class: |
524/492 ;
106/170.57; 106/197.01; 106/217.3; 106/287.34; 106/482;
106/491 |
Current CPC
Class: |
C09C 1/30 20130101; C01P
2006/12 20130101; C09C 1/3045 20130101; B41M 5/5218 20130101; C09D
7/61 20180101; C09D 17/007 20130101; C08K 3/36 20130101 |
Class at
Publication: |
524/492 ;
106/482; 106/491; 106/170.57; 106/197.01; 106/217.3;
106/287.34 |
International
Class: |
C09D 001/00; C09D
101/10; C08K 003/34 |
Claims
What is claimed is:
1. An aqueous dispersion comprising fumed silica particles,
colloidal silica particles, and water, wherein the fumed silica
particles have a BET surface area of about 70 to about 140
m.sup.2/g, the colloidal silica particles have a BET surface area
of about 110 to about 150 m.sup.2/g, the total amount of silica in
the dispersion is about 35% to about 60% by weight, and the fumed
silica particles comprise about 25% to about 80% by weight of the
total amount of silica in the dispersion.
2. The aqueous dispersion of claim 1, wherein the total amount of
silica in the dispersion is at least about 38% to about 60% by
weight.
3. The aqueous dispersion of claim 2, wherein the total amount of
silica in the dispersion is at least about 40% to about 60% by
weight.
4. The aqueous dispersion of claim 1, wherein the total amount of
silica in the dispersion is about 35% to about 50% by weight.
5. The aqueous dispersion of claim 1, wherein the fumed silica
particles have a BET surface area of about 80 to about 100
m.sup.2/g.
6. The aqueous dispersion of claim 1, wherein the colloidal silica
particles have a BET surface area of about 120 to about 140
m.sup.2/g.
7. The aqueous dispersion of claim 1, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
8. The aqueous dispersion of claim 7, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
9. The aqueous dispersion of claim 3, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
10. The aqueous dispersion of claim 9, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
11. A coating composition comprising at least one binder and the
aqueous dispersion of claim 1.
12. The coating composition of claim 11, wherein the total amount
of silica in the dispersion is at least about 38% to about 60% by
weight.
13. The coating composition of claim 12, wherein the total amount
of silica in the dispersion is at least about 40% to about 60% by
weight.
14. The coating composition of claim 11, wherein the total amount
of silica in the dispersion is about 35% to about 50% by
weight.
15. The coating composition of claim 11, wherein the fumed silica
particles have a BET surface area of about 80 to about 100
m.sup.2/g.
16. The coating composition of claim 11, wherein the colloidal
silica particles have a BET surface area of about 120 to about 140
m.sup.2/g.
17. The coating composition of claim 11, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
18. The coating composition of claim 17, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
19. The coating composition of claim 13, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
20. The coating composition of claim 19, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
21. The coating composition of claim 11, wherein the binder is
selected from the group consisting of cellulose esters, cellulose
ethers, starch, vinyl polymers, acrylic polymers, polyesters,
polycarbonate polymers, polyamides, polyimides, epoxy polymers,
phenolic polymers, polyolefins, copolymers thereof, and mixtures
thereof.
22. The coating composition of claim 21, wherein the binder is a
vinyl polymer selected from the group consisting of polyvinyl
alcohol, polyvinyl pyrrolidine, and mixtures thereof.
23. The coating composition of claim 11, wherein the total amount
of binder in the coating composition is about 0.5% to about 20% by
weight.
24. A recording medium comprising a substrate and a coating
composition applied to at least a portion of the substrate, wherein
the coating composition comprises at least one binder and an
aqueous dispersion comprising fumed silica particles, colloidal
silica particles, and water, and wherein the fumed silica particles
have a BET surface area of about 70 to about 140 m.sup.2/g, the
colloidal silica particles have a BET surface area of about 110 to
about 150 m.sup.2/g, the total amount of silica in the aqueous
dispersion is about 35% to about 60% by weight, and the fumed
silica particles comprise about 25% to about 80% (by weight) of the
total amount of silica in the dispersion.
25. The recording medium of claim 24, wherein the substrate is
paper.
26. The recording medium of claim 24, wherein the total amount of
silica in the dispersion is at least about 38% to about 60% by
weight.
27. The recording medium of claim 26, wherein the total amount of
silica in the dispersion is at least about 40% to about 60% by
weight.
28. The recording medium of claim 24, the total amount of silica in
the dispersion is about 35% to about 50% by weight.
29. The recording medium of claim 24, wherein the fumed silica
particles have a BET surface area of about 80 to about 100
m.sup.2/g.
30. The recording medium of claim 24, wherein the colloidal silica
particles have a BET surface area of about 120 to about 140
m.sup.2/g.
31. The recording medium of claim 24, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
32. The recording medium of claim 17, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
33. The recording medium of claim 27, wherein the fumed silica
particles comprise about 30% to about 80% by weight of the total
amount of silica in the dispersion.
34. The recording medium of claim 19, wherein the fumed silica
particles comprise about 50% to about 65% by weight of the total
amount of silica in the dispersion.
Description
FIELD OF THE INVENTION
[0001] This invention pertains to aqueous dispersions comprising
silica particles useful in the preparation of coating compositions
and recording media.
BACKGROUND OF THE INVENTION
[0002] A surface coating is sometimes applied to a recording medium
in order to improve its printing properties. For example, the
coating can improve the appearance, ink absorption, and/or image
smear resistance of the medium.
[0003] Surface coatings can be classified into two general
categories-glossy coatings and non-glossy (matte or dull) coatings.
Glossy coatings are often desirable, as they are very smooth, and
can impart a superior feel and a photograph-like quality to a
recorded image.
[0004] A coating composition comprising a pigment such as a
hydrated aluminosilicate (such as a kaolin clay), titanium dioxide,
alumina, silica, or calcium carbonate can be used to make a glossy
coating if the composition is applied by cast coating, wherein the
composition is dried while contacting a polished metal cylinder or
drum (e.g., a polished chromium drum). A glossy pigment coating
prepared in this manner is advantageous not only for its gloss, but
because the pigment can impart a relatively high rate and capacity
of ink absorption to the coating as well. However, the cast coating
procedure is relatively slow and costly.
[0005] It is possible to make glossy pigment coatings using
application methods which are cheaper and faster than cast coating
(e.g., bar coating, air-knife coating, roll coating, etc.,
sometimes followed by calendering), but the overall gloss of the
resulting coating is often diminished compared to cast coating.
Moreover, glossy pigment coatings prepared using these rapid,
inexpensive methods also can be quite brittle, and the coatings
often crack and flake upon drying.
[0006] Coating compositions comprising resins such as polyolefin
resin, polyester resin, polyamide resin, or polycarbonate resin can
be applied using the aforementioned rapid, inexpensive coating
methods (e.g., bar coating, air-knife coating, roll coating, etc.),
to form coatings having a high gloss. However, a recording medium
having such a glossy resin coating generally has significantly
decreased rates of ink absorption and ink drying compared to a
recording medium having a pigment coating.
[0007] A need exists for a recording medium having a coating that
can be applied using a rapid, inexpensive coating procedure,
wherein the coating is non-brittle, and wherein ink applied to the
recording medium is rapidly absorbed, and rapidly dries. A need
also exists for a coating composition that can be used in preparing
such a recording medium, and for a dispersion that can be used to
prepare such a coating composition. The invention provides such a
recording medium, coating composition, and dispersion.
BRIEF SUMMARY OF THE INVENTION
[0008] The invention provides an aqueous dispersion comprising
fumed silica particles, colloidal silica particles, and water. The
fumed silica particles have a BET surface area of about 70 to about
140 m.sup.2/g, the colloidal silica particles have a BET surface
area of 110 to about 150 m.sup.2/g, the total amount of silica in
the dispersion is at least about 35% to about 60% by weight, and
the fumed silica particles comprise about 25% to about 80% by
weight of the total amount of silica in the dispersion.
[0009] The invention also provides a coating composition comprising
at least one binder and the aqueous dispersion of the invention.
The invention further provides a recording medium comprising a
substrate and the coating composition of the invention applied to
at least a portion of the substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The invention provides an aqueous dispersion comprising
fumed silica particles, colloidal silica particles, and water,
wherein the fumed silica particles have a BET surface area of about
70 to about 140 m.sup.2/g, the colloidal silica particles have a
BET surface area of 110 to about 150 m.sup.2/g, the total amount of
silica in the dispersion is at least about 35% to about 60% by
weight, and the fumed silica particles comprise about 25% to about
80% by weight of the total amount of silica in the dispersion.
[0011] As utilized herein, the term "dispersion" means a suspension
of solid particles (e.g., fumed silica and colloidal silica) in a
liquid medium (e.g., water), wherein at least 95 wt. % (e.g., at
least about 97 wt. % or at least about 99 wt. %) of the total solid
particles in the liquid medium remain suspended in the liquid
medium (i.e., are colloidally stable in that the particles do not
settle to the bottom of a container) for at least about 24 hours
when the suspension is allowed to stand at a temperature of about
25.degree. C. following the preparation thereof.
[0012] Fumed silica particles, which are also referred to as
pyrogenic silica particles, are produced by pyrogenic processes and
have the chemical composition SiO.sub.2. Fumed silica particles,
typically, are aggregate particles of smaller primary particles,
which are held together by relatively strong cohesive forces, such
that the aggregate particles are not broken down into primary
particles when dispersed in a liquid (e.g., aqueous) medium.
Aggregate fumed silica particles may also form larger agglomerate
particles, which are held together by relatively weak cohesive
forces. Agglomerate particles usually are broken down into
aggregate particles when dispersed in a liquid (e.g., aqueous)
medium.
[0013] The surface area of most metal oxide particles can be
determined by the method of S. Brunauer, P. H. Emmet, and I.
Teller, J. Am. Chemical Society, 60, 309 (1938), which is commonly
referred to as the BET method. As noted above, fumed silica
particles suitable for use in the invention have a BET surface area
of about 70 to about 140 m.sup.2/g (e.g., about 80 to about 130
m.sup.2/g). In a preferred embodiment, the fumed silica particles
have a BET surface area of about 80 to about 100 m.sup.2/g (e.g.,
about 90 m.sup.2/g).
[0014] Colloidal silica particles are generally produced by "wet
chemistry" processes and also have the chemical composition
SiO.sub.2. Typically, colloidal silica is produced by the addition
of an acid to an alkaline metal silicate solution (e.g., sodium
silicate solution), thereby causing the silicate to polymerize and
form discrete particles of amorphous silica. Colloidal silica
particles, typically, are discrete, substantially spherical silica
particles having no internal surface area. Commercially available
colloidal silicas suitable for use in the invention include, but
are not limited to, those sold under the trademarks Ludox.RTM.
(Grace Davison), Bindzil.RTM. (Akzo Nobel), and Nyacol.RTM. (Akzo
Nobel). Colloidal silica particles suitable for use in the
invention have a BET surface area of 110 to about 150 m.sup.2/g. In
a preferred embodiment, the colloidal silica particles have a BET
surface area of about 120 to about 140 m.sup.2/g (e.g., about 130
m.sup.2/g).
[0015] Generally, the total amount of silica in the dispersion is
about 35% to about 60% (e.g., about 35% to about 55% or about 35%
to about 50%) by weight of the dispersion. Preferably, the total
amount of silica in the dispersion is about 38% to about 60% (e.g.
about 38% to about 55% or about 38% to about 50%), more preferably
about 40% to about 60% (e.g., about 40% to about 55% or about 40%
to about 50%) by weight of the dispersion. In another preferred
embodiment, the total amount of silica in the dispersion is about
35% to about 50% (e.g., about 35% to about 45%) by weight of the
dispersion.
[0016] Generally, the fumed silica particles comprise about 25% to
about 80% by weight of the total amount of silica in the
dispersion. In a preferred embodiment, the fumed silica particles
comprise about 30% to about 80% by weight, more preferably about
50% to about 65% by weight of the total amount of silica in the
dispersion.
[0017] As set forth above, a dispersion comprises particles
suspended in a liquid medium. The inventive aqueous dispersion
comprises water, preferably deionized water. The aqueous dispersion
also can comprise any number of suitable water-miscible liquids,
such as one or more water-miscible alcohols (e.g., methanol,
ethanol, etc.) or ketones (e.g., acetone) in addition to water.
[0018] The dispersion can have any suitable pH at which the
dispersion is stable. Typically, the pH of the dispersion is no
less than about 7 (e.g., about 7 to about 13), preferably no less
than about 8 (e.g., about 8 to about 12), more preferably no less
than about 9 (e.g., about 9 to about 11). In other embodiments, the
pH of the dispersion is no greater than about 13, preferably no
greater than about 12, and more preferably no greater than about
11. The pH of the dispersion can be adjusted using any suitable
method, such as via the addition of an acid (e.g., mineral acid,
acidic cation exchange resin, etc.) or a base (e.g., an alkali
metal hydroxide, basic anion exchange resin, etc.).
[0019] Generally, the dispersion of fumed silica particles,
colloidal silica particles, and water exhibits a relatively low
viscosity. The viscosity can be measured, for example, using a
Brookfield LVT viscometer (spindle no. 5, 60 rpm, two minute spin
at 25.degree. C.). Alternatively, the viscosity may be measured
pursuant to ASTM D 2196 (06.01) entitled "Rheological Properties of
Non-Newtonian Materials by Rotational (Brookfield) Viscometer."
Typically, the aqueous dispersion of the invention has a viscosity
of less than about 100 centipoise (cPs) (e.g., about 10 to about
100 cPs) immediately following the preparation thereof. Preferably,
the aqueous dispersion has a viscosity of less than about 75 cPs
(e.g., about 10 to about 75 cPs), more preferably less than about
50 cPs (e.g., about 15 to about 50 cPs), most preferably less than
about 30 cPs (e.g., about 15 to about 30 cPs) immediately following
the preparation thereof. In other embodiments, the aqueous
dispersion has a viscosity of at least about 5 cPs, preferably at
least about 10 cPs, more preferably at least about 15 cPs. It is
preferred that the viscosity of the dispersion increases by less
than about 50%, more preferably less than about 25%, most
preferably less than about 10% when the dispersion is allowed to
stand at a temperature of about 25.degree. C. for 60 days, 90 days,
180 days, and/or 270 days immediately following the preparation
thereof.
[0020] While the dispersion can contain other additives, in certain
applications it is preferred that the dispersion consists
essentially of, or consists of, fumed silica particles, colloidal
silica particles, and water. The phrase "consists essentially of,"
as used herein to describe the inventive dispersion, excludes any
component that would negatively impact the colloidal stability of
the aqueous dispersion (e.g., any component that would cause the
fumed silica particles and/or colloidal silica particles to settle
out of the dispersion).
[0021] The dispersion can be prepared by any suitable method.
Preferably, the dispersion is prepared by a method comprising (a)
mixing fumed silica particles with an aqueous vehicle under high
shear conditions to form a mixture of fumed silica particles, such
that the mixture does not coagulate, and (b) adding colloidal
silica particles to the mixture of (a), so as to form a dispersion
of fumed silica particles, colloidal silica particles, and water.
Mixing under high shear conditions provides an even distribution of
the components of the dispersion, thereby forming a substantially
uniform or homogeneous mixture of the components. Mixing under high
shear conditions also can improve the rheology of the dispersion
and can increase the strength and uniformity of any final article
prepared from the dispersion. High shear mixers are described in
U.S. Pat. Nos. 4,225,247, 4,552,463, 4,889,428, 4,944,595, and
5,061,319.
[0022] In a related aspect, the invention provides a coating
composition comprising at least one binder and the aqueous
dispersion of fumed silica particles, colloidal silica particles,
and water described herein. Any suitable binder(s) can be used in
accordance with the coating composition of the invention.
Preferably, the binder is selected from the group consisting of
cellulose esters, cellulose ethers, starch, vinyl polymers, acrylic
polymers, polyesters, polycarbonate polymers, polyamides,
polyimides, epoxy polymers, phenolic polymers, polyolefins,
copolymers thereof, and mixtures thereof. In another preferred
embodiment, the binder is a vinyl polymer selected from the group
consisting of polyvinyl alcohol, polyvinyl pyrrolidine, and
mixtures thereof.
[0023] The binder(s) can be present in the coating composition in
any suitable amount. Typically, the total amount of binder(s) in
the coating composition is less than about 20% (e.g., about 0.1% to
about 20% or about 0.5% to about 20%), preferably less than about
15% (e.g., about 0.5% to about 15%), more preferably less than
about 10% (e.g., about 1% to about 10%) by weight of the coating
composition. In other embodiments, the total amount of binder(s) in
the coating composition is greater than about 0.1%, preferably
greater than about 0.5%, more preferably greater than about 1% by
weight of the coating composition. The desired amount of binder(s)
in the aqueous dispersion depends on the particular binder(s). For
example, the optimum amount of polyvinyl alcohol in the coating
composition may be different from the optimum amount of polyvinyl
pyrrolidine in the coating composition.
[0024] The coating composition can be prepared by any suitable
method. Preferably, the coating composition is prepared by
combining an aqueous dispersion as described herein (e.g., an
aqueous dispersion comprising fumed silica particles, colloidal
silica particles, and water) with at least one binder to produce
the coating composition. The pH of the coating composition can be
adjusted at any stage during its preparation so as to prevent
flocculation and/or coagulation of the coating composition or any
component used to produce the coating composition (e.g., a
dispersion of fumed silica particles and colloidal silica
particles). For example, the pH can be adjusted during the
preparation of the dispersion before mixing the dispersion with the
binder(s). The pH also can be adjusted after the dispersion is
mixed with the binder(s) (i.e., after forming the coating
composition). In any case, it is preferred that the pH of the
coating composition be about 7 to about 13 (e.g., about 8 to about
12). In certain embodiments, such as when maximum dispersion
stability is desired, it is preferred that the pH of the coating
composition be about 9 to about 12, more preferably about 9 to
about 11 (e.g., about 9 to about 10). The pH can be adjusted using
any suitable method, such as via the addition of an acid (e.g.,
mineral acid, acidic cation exchange resin, etc.) or a base (e.g.,
an alkali metal hydroxide, basic anion exchange resin, etc.).
[0025] The coating composition of the invention also can comprise
one or more other additives, such as surfactants (e.g., cationic
surfactants, anionic surfactants such as longchain alkylbenzene
sulfonate salts and long-chain, preferably branched chain,
alkylsulfosuccinate esters, nonionic surfactants such as
polyalkylene oxide ethers of longchain, preferably branched-chain
alkyl group-containing phenols and polyalkylene oxide ethers of
long-chain alkyl alcohols, and fluorinated surfactants), hardeners
(e.g., active halogen compounds, vinylsulfone compounds, aziridine
compounds, epoxy compounds, acryloyl compounds, isocyanate
compounds, etc.), pigment dispersants, thickeners (e.g.,
carboxymethyl cellulose (CMC)), flowability improvers, antifoamers
(e.g., octyl alcohol, silicone-based antifoamers, etc.), foam
inhibitors, releasing agents, foaming agents, penetrants, coloring
dyes, coloring pigments, whiteners (e.g., fluorescent whiteners),
preservatives (e.g., p-hydroxybenzoate ester compounds,
benzisothiazolone compounds, isothiazolone compounds, etc.),
antifungal agents, yellowing inhibitors (e.g., sodium
hydroxymethanesulfonate, sodium p-toluenesulfinate, etc.),
ultraviolet absorbers (e.g., benzotriazole compounds having an
hydroxy-dialkylphenyl group at the 2-position), antioxidants (e.g.,
sterically hindered phenol compounds), antistatic agents, pH
regulators (e.g., sodium hydroxide, sodium carbonate, sulfuric
acid, hydrochloric acid, phosphoric acid, citric acid, etc.),
water-resisting agents, wet strengthening agents, and dry
strengthening agents. In addition to these additives, the coating
composition also can comprise a mordant. Suitable mordants include,
for example, poly(ethyleneimine), poly(vinylbenzyl
trimethylammonium chloride), poly(diallyldimethyl ammonium
chloride), and mixtures thereof.
[0026] The invention further provides a recording medium comprising
a substrate and a coating composition as described herein (e.g., a
coating composition comprising at least one binder and an aqueous
dispersion comprising fumed silica particles, colloidal silica
particles, and water) applied to at least a portion of the
substrate. The substrate used in conjunction with the invention can
be either transparent or opaque, and can be made of any suitable
material. Examples of such materials include, but are not limited
to, polyesters (e.g., poly(ethylene terephthalate)), diacetate
resins, triacetate resins, acrylic resins, polycarbonate resins,
polyvinyl chloride resins, polyimide resins, cellophane and
celluloid, glass sheets, metal sheets, plastic sheets, paper (e.g.,
cellulose or synthetic paper), photobase material (e.g., paper
coated with polyethylene or baryte), pigment-containing opaque
films, and foamed films. Preferably, the substrate comprises a
polymer film, paper, or a photo-base material. When the substrate
comprises a polymer film, the polymer film is preferably selected
from the group consisting of poly(ethylene terephthalate),
polyvinyl chloride, or mixtures thereof. When the substrate
comprises a paper, the paper is preferably cellulose paper, and
when the substrate comprises a photo-base material, preferably the
photo-base material is coated with at least one material selected
from the group consisting of polyethylene, baryte, and mixtures
thereof. Although the invention is well suited to the production of
gloss and semi-gloss recording media, the invention also can be
used to produce other types of recording media (e.g., recording
media having a matte finish).
[0027] The recording medium described herein can be prepared in
accordance with the invention by a method comprising (a) providing
a substrate, (b) providing a coating composition as described
herein (e.g., a coating composition comprising at least one binder
and an aqueous dispersion comprising fumed silica particles,
colloidal silica particles, and water), (c) coating at least a
portion of the substrate with the coating composition to provide a
coated substrate, and (d) drying the coated substrate to provide a
recording medium. Furthermore, the coating composition may be
repeatedly applied to the substrate to provide a recording medium
having a coating with a desired thickness.
[0028] Any suitable method can be used to coat a portion of the
substrate with the inventive coating composition. Suitable methods
include, but are not limited to, roll coating, blade coating, air
knife coating, rod coating (e.g., using a Meyer rod or the like),
bar coating, cast coating, gate roll coating, wire bar coating,
short-dowel coating, slide hopper coating, curtain coating,
flexographic coating, gravure coating, Komma coating, size press
coating in the manner of on- or off-machine, and die coating, with
rapid, inexpensive methods such as rod coating and blade coating
being preferred. The coating applied to the substrate can be of any
suitable thickness. In particular, the coating is preferably less
than about 50 .mu.m in thickness (e.g., about 1 to about 50 .mu.m),
more preferably less than about 40 .mu.m (e.g., about 5 to about 40
.mu.m), and most preferably less than about 30 .mu.m (e.g., about
10 to about 30 .mu.m). The coating also preferably is greater than
about 1 .mu.m, more preferably greater than about 5 .mu.m, most
preferably greater than about 10 .mu.m in thickness.
[0029] After application of the coating composition to the
substrate, the coated substrate can be dried using any suitable
method or combination of methods to provide the recording medium.
Suitable drying methods include, but are not limited to, air or
convection drying (e.g., linear tunnel drying, arch drying,
air-loop drying, sine curve air float drying, etc.), contact or
conduction drying, and radiant-energy drying (e.g., infrared drying
and microwave drying).
[0030] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLE 1
[0031] This example demonstrates the preparation of an aqueous
dispersion according to the invention. A high-shear mixer was
charged with 16.5 kg of water and 0.03 kg of a 37 wt. % HCl
solution. While the high-shear mixer was operating, 13.6 kg of
fumed silica particles having a BET surface area of about 90
m.sup.2/g (Cab-O-Sil.RTM. L-90, available from Cabot Corporation)
was slowly added to the water and HCl solution. Next, 7.1 kg of
water was added to the mixer, followed by approximately 0.48 kg of
a 45 wt. % KOH solution. Lastly, 18.8 kg of a 50 wt. % colloidal
silica dispersion containing colloidal silica particles having a
BET surface area of about 130 m.sup.2/g (Ludox.RTM. TM-50,
available from Grace Davison) was added to the mixture of water,
HCl, and fumed silica particles, and the mixer was stopped.
[0032] The product was a stable, aqueous dispersion comprising
fumed silica particles, colloidal silica particles, and water. The
aqueous dispersion had a total silica content of about 40% by
weight of the dispersion.
EXAMPLE 2
[0033] This example demonstrates the preparation of an aqueous
dispersion according to the invention. A high-shear mixer was
charged with 625 kg of water and 0.77 kg of a 37 wt. % HCl
solution. While the high-shear mixer was operating, 510 kg of fumed
silica particles having a BET surface area of about 130 m.sup.2/g
(Cab-O-Sil.RTM. LM-130, available from Cabot Corporation) was
slowly added to the water and HCl solution. Next, 305 kg of water
was added to the mixer, followed by approximately 19.2 kg of a 45
wt. % KOH solution. Lastly, 730 kg of a 50 wt. % colloidal silica
dispersion containing colloidal silica particles having a BET
surface area of about 130 m.sup.2/g (Ludox.RTM. TM-50, available
from Grace Davison) was added to the mixture of water, HCl, and
fumed silica particles, and the mixer was stopped.
[0034] The product was a stable, aqueous dispersion comprising
fumed silica particles, colloidal silica particles, and water. The
aqueous dispersion had a total silica content of about 40% by
weight of the dispersion.
EXAMPLE 3
[0035] This example demonstrates the preparation of an aqueous
dispersion according to the invention. A high-shear mixer was
charged with 235 g of water and 0.66 g of a 37 wt. % HCl solution.
While the high-shear mixer was operating, 217 g of fumed silica
particles having a BET surface area of about 90 m.sup.2/g
(Cab-O-Sil.RTM. L-90, available from Cabot Corporation) was slowly
added to the water and HCl solution. Next, 118 g of water was added
to the mixer, followed by approximately 20 g of a 45 wt. % KOH
solution. Lastly, 195 g of a 50 wt. % colloidal silica dispersion
containing colloidal silica particles havinga BET surface area of
about 130 m.sup.2/g (Ludox.RTM. TM-50, available from Grace
Davidson) was added to the mixture of water, HCl, and fumed silica
particles, and the mixer was stopped.
[0036] The product was a stable, aqueous dispersion comprising
fumed silica particles, colloidal silica particles, and water. The
aqueous dispersion had a total silica content of about 40% by
weight of the dispersion.
EXAMPLE 4
[0037] This example demonstrates the preparation of a coating
composition in accordance with the invention. All of the amounts
set forth in this example are expressed as parts per 100 g of the
final coating composition. A mixer was charged with 8.7 g of the
aqueous dispersion of Example 1. Next, while the mixer was
operating, 2.5 g of a commercially available starch binder
(Ethylex.RTM. 2025, available from A. E. Staley Manufacturing
Company) and 2.5 g of a commercially available polyvinyl alcohol
binder (Airvol.RTM. 523S, available from Air Products and
Chemicals, Inc.) were added to the mixer. The resulting mixture was
then diluted with 86.3 g of deionized water and mixed for an
additional 15 minutes.
[0038] The product was a coating composition comprising water, a
starch binder, a polyvinyl alcohol binder, and an aqueous
dispersion comprising fumed silica particles, colloidal silica
particles, and water. The coating composition contained 8.5% silica
by wieght of the coating composition. The coating composition had a
viscosity of approximately 20 cPs, as measured using a Brookfield
LVT viscometer (spindle no. 3, 20 rpm, two minute spin at
25.degree. C.).
EXAMPLE 5
[0039] This example demonstrates the preparation of a recording
medium in accordance with the invention. The coating composition of
Example 4 was applied to the surface of a cellulose paper substrate
using a #6 Meyer rod. The coated substrate was then dried at
107.degree. C. for approximately 5 minutes.
[0040] The product was a recording medium comprising a substrate
having a coating composition applied to at least a portion of the
substrate. The recording medium exhibited intense and vivid color
when printed with a test pattern consisting of blocks of black,
cyan, magneta, yellow, blue, green, and red (using a
Hewlett-Packard PhotoSmart.RTM. 1210 inkjet printer).
[0041] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0042] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any nonclaimed element as essential to the practice of
the invention.
[0043] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *